The boss of Goldman Sachs has waded in to the debate over Brexit by issuing another veiled threat about the Wall Street firm’s employment plans in London as a result of the UK’s vote to leave the EU.

Lloyd Blankfein sent a tweet of an aerial shot of the new £350m European headquarters the bank has under construction in London, with the words “expecting/hoping to fill it up, but so much outside our control”.

It had already begun work on a new European headquarters in London before the referendum in June 2016 and the 10-storey building is scheduled for completion in March 2019 – just as the UK is due to leave the EU.

Goldman Sachs employs 6,000 staff in three premises in London and has the option to take all the space in the new building – just a stone’s throw from its main London location in Fleet Street – or sublet space. Goldman has yet to disclose how many staff will be located in the new building.

Just left Frankfurt. Great meetings, great weather, really enjoyed it. Good, because I'll be spending a lot more time there. #Brexit

Many in the City are watching Goldman’s occupancy plans for the new London headquarters as a gauge for the impact of Brexit on the financial centre. The Frankfurt building could house up to 1,000 staff – suggesting the prospect of adding 800 on top of the 200 already employed in the German financial centre.